Thankfully, this wouldn't be a perfect crime - there are several weaknesses that each (thankfully) provide many opportunities for police to collect evidence. For example, Boris and Oleg would need to conduct the exercise (for lack of a better euphemism) somewhere they control yet that cannot be tied back to them. They would need to keep the scene extraordinarily clean since the types of people who would torture are often the types of people with DNA samples in databases. They would have to avoid each other's names. And, faced with the prospect of serious jail time (this crime would receive a life sentence in many parts of the world), each party to the offense would have to stay solid.

The curse of intelligent criminals is all powerful. Intelligent criminals have to get lucky every single day for the rest of their lives. The police only need to get lucky once!! :)

That was a fun thought exercise and I hope your deserved upvotes rain in.